The speed of field effect transistors (FETs) is closely related to the drive currents of the FETs, which drive currents are further closely related to the mobility of charges. For example, NFETs have high drive currents when the electron mobility in their channel regions is high, while PFETs have high drive currents when the hole mobility in their channel regions is high. Compound semiconductor materials of group III and group V elements (known as III-V compound semiconductors) are good candidates for forming transistors due to their high electron mobility. Therefore, transistors formed on III-V compound semiconductors have been explored.
III-V compound semiconductor films, however, typically need to be grown on other substrates because it is difficult to obtain bulk III-V crystals. The growth of III-V compound semiconductor films on dissimilar substrates faces difficulties because these substrates have lattice constants and thermal expansion coefficients different than that of the III-V compound semiconductors. Various methods have been used to form high-quality III-V compound semiconductors that do not suffer from severe defects. For example, III-V compound semiconductors were grown from trenches between shallow trench isolation (STI) regions to utilize aspect ratio trapping (ART) to trap defects at the bottom of a III-V compound semiconductor film and to prevent defect propagation to a surface region.
Some structures using III-V compound semiconductors grown on dissimilar substrates in trenches between STI regions may integrate one III-V compound semiconductor grown on a different III-V compound semiconductor. In these instances, even with reduced defects at the surface region due to ART, defects, e.g., planar defects, may be generated by growing the III-V compound semiconductor on the different III-V compound semiconductor.